antigallican Posted August 10, 2017 Share #1 Posted August 10, 2017 (edited) Advertisement (gone after registration) I found something interesting today. Focussed on a book a little over 2 metres away the metrics given on the oled for 90mm zoom at f4 are back 2.44 focus 2.41 front 2.38. At 24mm f2.8 they are back 2.54 focus 2.22 front 1.98. Both of these are single point focus with the green 'focus confirmation' lit. Of course this suggests DOF 6cm at f4 90mm and 56cm at f2.8 24mm. It's more or less what would expect - on a wide angle lens nearly everything is in focus nearly all the time - but this is the first camera I've had which gives you the figures ( unless it's hidden in the exif somewhere on dslrs). An inch and a bit either side of the focus point is just fine for the 90mm portrait. If you come down to 90mm f4 at about 1.5m you get back 1.52 focus 1.5 front 1.49. What does all this mean? It implies reviewers who want this sort of lens to be constant f stop are talking out of their hat when it comes to dof. Those guys in Wetzlar knew that. Maybe the stop or two of light transmission would matter if you didn't have that little bar in the evf telling you you are under or over exposing. Ps it was Cira's post which provoked me to experiment Edited August 10, 2017 by antigallican Quote Link to post Share on other sites More sharing options...
Advertisement Posted August 10, 2017 Posted August 10, 2017 Hi antigallican, Take a look here DOF, 24-90 and the 601. I'm sure you'll find what you were looking for!
01af Posted August 10, 2017 Share #2 Posted August 10, 2017 I found something interesting today. [...] Where's the interesting part? Quote Link to post Share on other sites More sharing options...
antigallican Posted August 10, 2017 Author Share #3 Posted August 10, 2017 It flushes out all the little spassvogels Quote Link to post Share on other sites More sharing options...
earleygallery Posted August 10, 2017 Share #4 Posted August 10, 2017 Not sure what your point is. Constant f stop is important for photographers who want so use manual exposure and don't want to adjust it every time they move the zoom. Dof is something entirely different. Quote Link to post Share on other sites More sharing options...
antigallican Posted August 10, 2017 Author Share #5 Posted August 10, 2017 Hi James, my point is that people think 'f4, slow lens, I need shallower DOF for portrait etc'. Actually the 24-90's DOF is 6cm (just over 2 inches) at at 90mm zoom and f4, 2.5 meters distance. I was quite surprised by the numbers. Quote Link to post Share on other sites More sharing options...
knisely Posted August 10, 2017 Share #6 Posted August 10, 2017 (edited) That is interesting. Sometimes I grab the 75mm Leica because I think f4 will have too deep a focus range. Edited August 10, 2017 by knisely 2 Quote Link to post Share on other sites More sharing options...
antigallican Posted August 10, 2017 Author Share #7 Posted August 10, 2017 Advertisement (gone after registration) That is interesting. Sometimes I grab the 75mm Leica because I think f4 will have to deep a focus range. Thanks Knisely, you've expressed concisely what I'd managed to mangle! Quote Link to post Share on other sites More sharing options...
LD_50 Posted August 10, 2017 Share #8 Posted August 10, 2017 I like constant aperture for light gathering ability for AF and for setting manual exposure and not having to tweak ISO or shutter speed if framing by zooming. I'm okay with the compromise for IQ, size, and weight with the SL lenses so far. 1 Quote Link to post Share on other sites More sharing options...
panoreserve Posted August 11, 2017 Share #9 Posted August 11, 2017 No problem - just activate "floating iso" and everything is fine... 1 Quote Link to post Share on other sites More sharing options...
thighslapper Posted August 11, 2017 Share #10 Posted August 11, 2017 Hi James, my point is that people think 'f4, slow lens, I need shallower DOF for portrait etc'. Actually the 24-90's DOF is 6cm (just over 2 inches) at at 90mm zoom and f4, 2.5 meters distance. I was quite surprised by the numbers. I have always found the 75/2, 90/2 and Noctilux useless for portraits wide open as DOF is so shallow you either get nose, eyes or ears in focus but hardly ever even two out of the 3, let alone the lot..... unless you deliberately want almost everything OOF, which has always struck me as having limited appeal. As you say, f4 or (or 2.8) is plenty shallow enough to isolate the subject from the background. 1 Quote Link to post Share on other sites More sharing options...
antigallican Posted August 12, 2017 Author Share #11 Posted August 12, 2017 (edited) No problem - just activate "floating iso" and everything is fine... floating iso just makes me feel there's one too many variable. f2.8, f4... at 24mm one stop barely matters because a 24mm lens usually has most things in focus. Hyperfocal focussing and all that. The hyperfocal distance at f4 on a 24mm lens is 5 metres, meaning at f4 everything from 2.5 metres to infinity is for practical purposes 'sharp'. So you may find it more convenient to set the lens to f4 and zoom to whatever focal length you want rather than use floating iso. Sent from my iPhone using Tapatalk Edited August 12, 2017 by antigallican Quote Link to post Share on other sites More sharing options...
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